Abstract
Sodium reabsorption through the epithelial sodium channel (ENaC) at the distal segment of the kidney plays an important role in salt-sensitive hypertension. We reported previously that hydrogen peroxide (H2O2) stimulates ENaC in A6 distal nephron cells via elevation of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) in the apical membrane. Here we report that H2S can antagonize H2O2-induced activation of ENaC in A6 cells. Our cell-attached patch-clamp data show that ENaC open probability (PO) was significantly increased by exogenous H2O2, which is consistent with our previous finding. The aberrant activation of ENaC induced by exogenous H2O2 was completely abolished by H2S (0.1 mM NaHS). Pre-treatment of A6 cells with H2S slightly decreased ENaC PO; however, in these cells H2O2 failed to elevate ENaC PO. Confocal microscopy data show that application of exogenous H2O2 to A6 cells significantly increased intracellular reactive oxygen species (ROS) level and induced accumulation of PI(3,4,5)P3 in the apical compartment of the cell membrane. These effects of exogenous H2O2 on intracellular ROS levels and on apical PI(3,4,5)P3 levels were almost completely abolished by treatment of A6 cells with H2S. In addition, H2S significantly inhibited H2O2-induced oxidative inactivation of the tumor suppressor phosphatase and tensin homolog (PTEN) which is a negative regulator of PI(3,4,5)P3. Moreover, BPV(pic), a specific inhibitor of PTEN, elevated PI(3,4,5)P3 and ENaC activity in a manner similar to that of H2O2 in A6 cells. Our data show, for the first time, that H2S prevents H2O2-induced activation of ENaC through a PTEN-PI(3,4,5)P3 dependent pathway.
Highlights
The epithelial sodium channel (ENaC) mediates Na+ absorption across epithelial cells in the kidney collecting duct, lung, distal colon, and sweat duct
These results suggest that H2S exerts a strong protective effect on H2O2-induced enhancement of ENaC activity in A6 cells
We have shown that H2O2 stimulates ENaC [6], which plays a key role in maintaining Na+ homeostasis and controls systemic blood pressure
Summary
The epithelial sodium channel (ENaC) mediates Na+ absorption across epithelial cells in the kidney collecting duct, lung, distal colon, and sweat duct. Overactivation of ENaC causes hypertension, as seen in Liddle’s syndrome [1]. It remains unclear whether enhanced ENaC activity accounts for salt-sensitive hypertension. High salt intake leads to an increase in the production of reactive oxygen species (ROS) including superoxide (O22) [2] and H2O2 [3] in the kidney by stimulating NAD(P)H oxidase [4]. ROS play an important role in signal transduction and have been shown to influence ENaC activity. One example is that aldosterone can regulate ENaC activity by elevating superoxide (O22) production in A6 cells [5]
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